It has been long known that certain phosphate esters are useful in generating gelled liquids, particularly gelled hydrocarbons. Gelled hydrocarbons, due to their high viscosity and ability to suspend solids, have found several applications in the field of oil recovery. More commonly they are used in stimulation related processes.
Several patents have been issued based on this concept, see for example U.S. Pat. Nos. 4,153,649, 4,622,155, 5,057,233, 5,190,675, and 6,261,998.
Despite the effectiveness of gelled liquid hydrocarbons in forming fractures in subterranean formations, one particular problem with their use has been described in literature. It has been reported that refineries processing oil produced from formations fractured with gelled liquid hydrocarbons have experienced fouling of the distillation towers. Analysis of the fouling material has revealed a high phosphorus content which has been postulated to originate from a phosphate ester distilling at 230-290° C. In response, several patents have been issued for formulations that are claimed to have low volatile phosphorus contribution in the distillate, see U.S. Pat. Nos. 7,066,262, 6,511,944, and US Applications 20070032387 and 20070173413. It has been speculated in the patent literature that decomposition of phosphate esters to lower molecular weight phosphorus compounds and/or the presence of certain low boiling impurities in the commercial mixture are the sources of volatile phosphorus species. Therefore, the use of less volatile trialkyl phosphate in the manufacturing process of the phosphorus based gelling agent as well as the replacement of phosphate esters with monoalkanephosphonic acid monoesters has been suggested as a method to ameliorate the fouling.
A number of studies on the pyrolysis and combustion of phosphate esters and alkylphosphonate esters have been published, see for example, H. E. Baumgarten, R. A. Setterquist J. Am. Chem. Soc. 1957, 79, 2605-2608 and P. A. Glaude, H. J. Curran, W. J. Pitz, C. K. Westbrook Kinetic Study of the Combustion of Phosphorus Containing Species, Article presented at 1999 Fall Meeting of the Western State Section of the Combustion Institute, Irvine, Calif., Oct. 25-26, 1999, and the references therein.
At elevated temperatures and in the presence of oxygen both phosphates and phosphonates decompose to P2O5 (solid) along with CO, CO2, H2O, C and CH4. In the absence of oxygen, P2O5 along with olefins are produced. P2O5 is the product of dehydration of H3PO4, neither of which can be distilled under atmospheric pressure (Erwin Riedel, Anorganishe Chemie, 5th edition, 2002, pp. 492-495 and Ch. E. Housecroft, A. G. Sharpe, Inorganic Chemistry first edition, 2001, pp 341-342).